The invention relates to vehicles for industrial and agricultural use, such as utility tractors. Particularly, the invention relates to speed control of a utility vehicle that incorporates a hydrostatic transmission as an operator-controlled speed-adjusting component of the vehicle drive train.
Agricultural or industrial utility vehicles typically utilize a drive train having an engine driving a hydrostatic transmission that drives a final drive transmission or range transmission of the vehicle. The final drive transmission drives at least one wheel. JOHN DEERE Series 4000 tractors, available from John Deere Commercial Products, include such drive trains. The vehicle speed is typically operator-modulated by changing the drive ratio of the hydrostatic transmission via movement of a foot pedal. The drive ratio is changed by changing the angle of a swashplate of a variable displacement pump of the hydrostatic transmission.
In the operation of tractors or other self-propelled machinery using hydrostatic transmissions, the maximum speed of operation is often limited to some value less than the full speed capacity of the vehicle. The operator modulates speed to any value less than the selected maximum speed. The operator performs the speed modulation control manually by adjusting foot pedal position. Given the entire pedal position range from a minimum speed up to the maximum speed, a precise modulation of the speed within a narrow speed tolerance between the minimum and maximum speeds is difficult to achieve. Attempting to modulate accurately at a precise speed between the minimum and maximum speeds is fatiguing to the operator, particularly to the operator""s leg.
A partial solution to this problem is a kit, available from John Deere Commercial Products for current JOHN DEERE 4000 Series tractors, that provides an adjustable mechanical stop to limit foot pedal travel and thus limit the maximum speed of the tractor. This solution however, cannot adjust to changes in engine speed, nor is it easy to adjust for changes in working conditions. This technique is also not effective for ground speed control in systems using hydrostatic transmissions that lack swashplate position feedback control.
The present inventors have recognized the desirability of providing an adjustable maximum speed control which accurately sets a maximum speed, corresponding to a terminal pedal position, and which allows effective operator speed modulation st speeds less than the set maximum speed.
Additionally, the present inventors have recognized that when operating tractors or other self-propelled machines in which the speed is controlled by a foot pedal or other manual means, it would be desirable to improve the sensitivity of the speed control for better xe2x80x9cinchingxe2x80x9d control, i.e., moving the machine very small distances and/or at very slow speeds.
A control system is provided for setting a set maximum speed of a utility vehicle, below the capable maximum speed of the vehicle, and recalibrating speed output signals corresponding to the set maximum speed. The system includes a microcontroller and a user-operated vehicle speed actuator, signal-connected to the microcontroller. The speed actuator moves over a limited mechanical range between a start end stop and a terminal end stop, and is calibrated to actuate speeds, via the microcontroller, in a range from a minimum speed to a maximum speed. The maximum speed corresponds to the terminal end stop.
A user-operated speed set activator is used in conjunction with a ground speed sensor to set the maximum speed. The ground speed sensor is signal-connected to the microcontroller, wherein, when initiated by the user, the activator causes the microcontroller to record the instantaneous ground speed signal from the sensor. The microcontroller sets a new maximum speed of the vehicle, the new maximum speed set to the instantaneous ground speed and the pedal position is recalibrated such that the new maximum speed corresponds to the pedal position at the terminal end stop. The microcontroller recalibrates the speed commands issued by the microcontroller to the servo control of the transmission, to be in a range from the minimum speed corresponding to the start end stop to the new maximum speed corresponding to the terminal end stop.
The speed set activator is operable to set a maximum speed for both forward and reverse vehicle operation.
The present invention uses speed control foot pedals with potentiometer sensors, a Hall effect sensor that measures the speed of a gear in the final drive of the transmission, on/off switches, a microcontroller and software. The invention provides a system and method for recalibrating the full pedal range of motion to provide for increased sensitivity of the speed control.
A method of controlling a ground speed of a utility vehicle is set forth. The method is adapted to control speed of a utility vehicle having an engine coupled to a transmission, the transmission coupled to a driven wheel, and a speed actuator movable over an actuator range to a terminal end stop, the actuator calibrated to drive the vehicle at speeds between a minimum speed and a maximum speed, the maximum speed corresponding to the terminal end stop. The method includes the steps of: during running out of the vehicle, selecting an instantaneous ground speed; setting a new maximum vehicle ground speed at the instantaneous ground speed; and recalibrating the actuator range from the minimum speed to the new maximum speed, the new maximum speed corresponding to the terminal end stop.
The operation of the maximum speed function according to the preferred embodiments is more particularly set forth as follows: an on/off switch is positioned to activate the use of the maximum speed function in the microcontroller software. Using the foot pedal controls on the vehicle, the operator drives the vehicle to the maximum speed limit desired for the specific task. Once at the desired maximum speed, a second switch is momentarily depressed and the microcontroller records the speed present in the final drive of the transmission from a Hall effect pulse pickup unit, as a new maximum speed limit. When the operator then releases the control pedal, the vehicle stops and the software becomes temporarily recalibrated so that the recorded new maximum speed limit is achieved with full foot pedal depression. The maximum speed limit can be increased or decreased incrementally during operation by momentarily depressing switches. To prevent the operator from disabling all vehicle motion, the algorithm requires the speed limit to be greater than zero. Moving the maximum speed switch to the off position disables the maximum speed limit function.
The vehicle response is scaled to the set maximum speed. In normal operation, the software in the microcontroller controls the ground speed from zero to the top vehicle speed as a preselected relationship to the pedal position input. When the maximum speed function is engaged, the relationship is rescaled to provide the new maximum set speed corresponding to a fully depressed pedal position. The new ground speed is thereafter controlled by a software control loop using the Hall effect pulse pickup signal for feedback control.
By basing the maximum speed limit on a measured transmission gear speed and using feedback control techniques, the speed limit control becomes insensitive to engine speed, terrain, attachment loading and gear selection. The driver can modulate the speed of the vehicle to any value less than the set maximum speed limit and return to the desired maximum speed limit simply by depressing the speed control pedal to its full travel. Preferably, the set maximum speed limit is the desired substantially constant operating speed. Holding the pedal in its fully depressed position is less fatiguing than having to hold the pedal partially depressed.
A second benefit to the maximum speed function is improved speed control sensitivity. The speed control software can be recalibrated according to a new maximum speed, substantially reduced from the actual maximum speed of the vehicle, so that each increment (inch or mm) of resulting pedal travel represents less speed change than when the maximum speed function is inactive. This permits the driver to optimize his control of the speed and position of the vehicle when attaching implements or working in close spaces.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.